We propose to study the role of plasma membrane-bound platelet enzymes in platelet function. We have identified two membrane-bound enzymes. One is a pyridine nucleotide dependent reductase which is inhibited by several inhibitors of platelet aggregation. The other is an amidase capable of hydrolyzing leucine-p-nitroanilide. The amidase can be released from the membrane by ADP or thrombin indicating that it is released during platelet aggregation and/or the ensuing release reaction. Further studies on the kinetic properties of these enzymes are planned in order to determine the physiological substrate of these enzymes as well as their role in platelet function.